In many parts of the world due to inadequate rainfall it is necessary at some times during the year to artificially water turf and landscaping. An ideal irrigation system for turf and landscaping should utilize a minimum number of valves, supply lines and sprinklers. Preferably the valves should be turned ON and OFF by an inexpensive, yet reliable electronic irrigation controller that is easy to program and can carry out a wide variety of watering schedules. The goal is to uniformly distribute the optimum amount of water over a given area. Rotor type sprinklers have largely displaced older impact type sprinklers in applications where large expanses of grass are watered, such as golf courses, due to the fact that the former are more reliable, quieter, and distribute water on a uniform and controlled basis. Spray type sprinklers, rotary stream sprinklers, bubblers and drip irrigation devices are also frequently used in residential and commercial irrigation systems. When an irrigation system is designed and/or installed the type, placement and precipitation rates for each of the sprinklers are pre-selected. The optimum precipitation rate provided by each sprinkler should preferably fall within plus or minus one-quarter gallons-per minute (GPM). The amount of water supplied by each sprinkler is largely determined by the size and configuration of its nozzle orifice(s), although variations result from fluctuations in water pressure that cannot be fully negated with regulators.
Preferably an irrigation controller should have the capability of temporarily terminating its watering program if sufficient rain occurs based on signals inputted from a rain sensor. See for example U.S. Pat. No. 5,097,861 granted Mar. 24, 1992 of Hopkins et al. entitled IRRIGATION METHOD AND CONTROL SYSTEM, assigned to Hunter Industries, Inc., the assignee of the subject application, the entire disclosure of which is hereby incorporated by reference. On suitable rain sensor for this purpose is disclosed in pending U.S. patent application Ser. No. 10/053,100 filed Oct. 26, 2001 of Paul A. Klinefelter et al. entitled QUICK SHUT-OFF EXTENDED RANGE HYGROSCOPIC RAIN SENSOR FOR IRRIGATION SYSTEMS, now U.S. Pat. No. 6,570,109 granted May 27, 2003, also assigned to Hunter Industries, Inc., the entire disclosure of which is hereby incorporated by reference.
Residential and commercial irrigation systems typically include one or more solenoid operated valves that are turned ON and OFF by an electronic irrigation controller. The valves admit water to various subterranean branch lines usually made of PVC pipe that typically have several sprinklers connected to risers coupled to the branch-lines at spaced intervals. Each combination of a solenoid valve and its associated sprinklers is referred to in the irrigation industry as a station or zone. A modern electronic irrigation controller typically includes a microprocessor and separate memory, or a micro-computer with on-chip memory, that stores and executes one or more watering programs. The watering programs can be pre-programmed by the user via push button and/or rotary controls. The controller usually has an LCD or other display to facilitate programming by the user. Often the controller will revert to a default watering program in the case of a power failure. The microprocessor controls the solenoid valves via suitable drivers and switching devices. The valves are opened and closed by the microprocessor in accordance with the pre-programmed run and cycle times for each of the stations.
Over the past decade, modular expandable irrigation controllers have gained increasing popularity. In these controllers, the base portion of the system contains the microprocessor and user actuated controls. Each station is then controlled by a corresponding station module which comprises a plastic housing that encloses and supports a station module circuit, as well as wire connection terminals for connecting wires to a plurality of solenoid actuated valves. Typically each station module can independently control more than one solenoid actuated valve, i.e., station. The station modules contain pins, sockets, card edge connectors or some other standard form of electro-mechanical connectors for allowing them to be inserted into slots or receptacles in either the housing that contains the microprocessor or a separate back panel hinged to the microprocessor housing. The advantage of this configuration is that the controller need only be equipped with the minimum number of station modules that can control the total number of stations. Thus, for example, an irrigation system may have only three zones, requiring only a single station module, while another may have twelve stations which might require four station modules. Considerable cost savings are thus achieved. Moreover, if an irrigation system expands after initial installation because the landscaping has increased, additional station modules can be added. In some modular expandable irrigation systems the base unit is capable of controlling a minimal number of stations without requiring the addition of any station modules. In others, such as the ICC™ and Pro C™ irrigation controllers manufactured and sold by Hunter Industries, Inc., at least a power module and one irrigation station module must be plugged into the controller in order to operate any stations or zones.
When the station modules are plugged into the receptacles of a modular expandable irrigation controller they are mechanically supported and an electrical connection is made between the microprocessor and the driver. The station modules can be removed and replaced if damaged, for example, during a lightening strike. It has been conventional to use plastic spring members or elements to hold the station modules in place in their respective receptacles or slots. However, such springs often require considerable force to be exerted by the user, both during installation and withdrawal of the station modules. The spring members can also break and difficulties have been encountered in ensuring that a complete and positive electrical connection is both achieved and maintained. In some cases, station module installation can lead to breakage in the metal pins or metal leaf spring contacts used to make the electrical connection.
Accordingly, it would be desirable to provide a modular expandable irrigation controller with improved station module mating to minimize or eliminate the foregoing problems.